There is a desire in the industry for higher circuit density in microelectronic devices which are made using lithographic techniques. One method of increasing the number of components per chip is to decrease the minimum feature size on the chip, which requires higher lithographic resolution. The use of shorter wavelength radiation (e.g. deep UV e.g. 190 to 315 nm) than the currently employed mid-UV spectral range (e.g. 350 nm to 450 nm) offers the potential for higher resolution. However, with deep UV radiation, fewer photons are transferred for the same energy dose and higher exposure doses are required to achieve the same desired photochemical response. Further, current lithographic tools have greatly attenuated output in the deep UV spectral region.
In order to improve sensitivity, several acid catalyzed chemically amplified resist compositions have been developed such as those disclosed in U.S. Pat. No. 4,491,628 (Jan. 1, 1985) and Nalamasu et al., "An Overview of Resist Processing for Deep-UV Lithography", J. Photopolym Sci. Technol. 4,299 (1991). The resist compositions generally comprise a photosensitive acid generator and an acid sensitive polymer. The polymer has acid sensitive side chain (pendant) groups which are bonded to the polymer backbone and are reactive towards a proton. Upon imagewise exposure to radiation, the photoacid generator produces a proton. The resist film is heated and, the proton causes catalytic cleavage of the pendant group from the polymer backbone. The proton is not consumed in the cleavage reaction and catalyzes additional cleavage reactions thereby chemically amplifying the photochemical response of the resist. The cleaved polymer is soluble in polar developers such as alcohol and aqueous base while the unexposed polymer is soluble in nonpolar organic solvents such as anisole. Thus the resist can produce positive or negative images of the mask depending on the selection of the developer solvent.
Although these resist compositions generally have suitable lithographic sensitivity, their performance can be impaired in the presence of airborne basic chemical contaminants which are present in a manufacturing site. MacDonald et al. SPIE 1466 2. (1991) reported that due to the catalytic nature of the imaging mechanism, acid catalyzed, chemically amplified resist systems are sensitive towards minute amounts of airborne basic organic chemical contaminants. These substances degrade the resulting developed image in the film and cause a loss of the linewidth control of the developed image. This problem is exaggerated in a manufacturing process where there is an extended and variable period of time between applying the film to the substrate and development of the image. In order to protect the resist from such airborne contaminants, the air surrounding the film is carefully filtered to remove such substances. Alternatively, the resist film is overcoated with a protective polymer layer. However, these are cumbersome processes.
Therefore, there still is a need in the art for a chemically amplified photoresist composition having stability in the presence of airborne basic chemical contaminants for use in semiconductor manufacturing.
It is therefore an object of the present invention to provide an improved chemically amplified photoresist composition for use in semiconductor manufacturing.
Other objects and advantages will become apparent from the following disclosure.